My husband is an industrial/commercial electrician (and now a general contractor!). He said it won't hurt anything, but he wouldn't advise doing it, as they do get warm. Not a fire hazard, but why would you want to leave it plugged in, as it will draw electricity the whole time it is plugged in. ($)
The little black box is a transformer that changes the 120 volts from the outlet to 9-12 volts, maybe, so the shock you could get is minimal.
I just unplugged mine. I keep it plugged in so I won't lose it. BUT as high as my electric bill has been I am doing all I can to conserve. I replaced ALL the bulbs in my house with the LEF bulbs. I haven't received my new bill yet to see if they have helped any. Does anyone else use them? Have they lowered your bill?
There's a fine line between genius and insanity. I have erased this line.